The present invention generally relates to Intelligent Electronic Devices (“IED's”) and more specifically, to the design and manufacture of a digital power meter. A typical digital power meter is described in U.S. Pat. No. 6,185,508.
One aspect of modern digital power meters is that many of them contain Flash EEPROM memory for storing their firmware, e.g. operating software. This allows the customer to upgrade the firmware in their device. Reasons for upgrading the firmware include adding new features, or correcting defects in the firmware code.
A number of methods for upgrading the firmware within the flash memory of IED's are known in the art. Typically they involve a CPU in a computer sending packets containing the update code to the IED over a communications channel. An example of this method of firmware updating is described in the document entitled “Meter Shop User's Guide”, published by Power Measurement Ltd., located in Saanichton, B.C., Canada.
The upgrade of the IED's firmware is normally initiated by the remote CPU (in a computer or other device). Therefore, the IED is not normally involved in the decision as to whether to upgrade its firmware or not. This means that the IED cannot prevent an undesirable upgrade to its code, e.g., if it is in the middle of a critical control operation, or if the new code is not compatible with the IED for some reason. In addition, there must be some intelligence in the remote CPU in order to execute the upgrade and/or provide an interface to the user that is initiating the upgrade. The user must also have intimate knowledge about the new code to ensure it is compatible with the IED.
Another key aspect of IED's is expandability. It is quite common for a user to want to add additional functionality to the device once it has been installed. Typically this will be additional functionality that requires a code change as described above or a change that requires additional hardware. If the change requires additional hardware, the device must often be replaced or at least removed from its installation to add the new hardware component.
Yet another key aspect of IED's is cost. There are many aspects of cost, but two key aspects are initial cost of a basic device and the cost to upgrade a device. Typical IED's contain complex processor, memory, analog to digital conversion, analog, digital and display circuitry which in many cases is either limited in functionality or formed out of many individual components. In addition, the purchaser of an IED must decide at the time of purchase the amount of functionality they want to have in their IED. An IED with a large amount of functionality will typically cost many times that of one with a limited amount of functionality.
Due to the desire to reduce the cost of the IED, it is common to use components which have reduced capabilities in terms of performance, accuracy, etc. This can lead to a final device which also has reduced performance, accuracy, etc.